PAL SYSTEM TELEVISION MEASUREMENT : APPENDIX A: PAL COLOUR BARS

APPENDIX A: PAL COLOUR BARS

There are several varieties of PAL colour bars, three of which are in common use. These three varieties, shown in Figure 109, are frequently referred to as 100% colour bars, 95% colour bars, and EBU colour bars. In this case, the 100% and 95% distinction refers to saturation, however, this convention is not universal. The maximum amplitudes of the R, G and B signals are also sometimes used to describe the various types of bars. (Recall from page 9 that Tektronix vectorscopes use the 75%/100% designation to
refer to amplitude.)

Figure 109. Waveforms and RGB voltages for three types of PAL colour bars.

Nomenclature.

It is confusing to use a single number to distinguish between the various types of colour bars, particularly if it is not clear which parameter that number describes. Furthermore, a single number is inadequate to

completely and uniquely define a given signal. For these reasons, a four-parameter system of colour bar specification has been developed. The following four parameters are used to describe the signal:

(a) Maximum value of ER´, EG´ or EB´ for an uncoloured bar.

(b) Minimum value of ER´, EG´ or EB´ for an uncoloured bar.

(c)Maximum value of ER´, EG´ or EB´ for a coloured bar.

(d)Minimum value of ER´, EG´ or EB´ for a coloured bar.

ER´, EG´ and EB´ are the three colour signals. Each parameter is specified as a percentage of the maximum voltage excursion allowable for PAL colour signals, which is 700 millivolts.

With this system of nomenclature, the three common types of bars can be uniquely described as 100.0.100.0 bars, 100.0.100.25 bars, and 100.0.75.0 bars. These numbers can readily be corre l a t e d with the Red, Green and Blue signals corresponding to each type of colour bars (see Figure 109).

Saturation.

Note that saturation is not included in this list of parameters. Saturation is a particularly difficult parameter

to use for uniquely specifying a colour bar signal because it depends on the value of Gamma.

Saturation is calculated as follows:

Saturation(%) = [1— (Emin/Emax) g ] x 100

Thus 100.0.100.25 colour bars have a saturation value of 95% if a value of 2.2 is used for Gamma. However, CCIR standards currently call for a Gamma value of 2.8 which yields a saturation value of 98% for 100.0.100.25 bars. Clearly, then, the saturation nomenclature is best avoided altogether.

Lihat juga

Table of Contents

Preface	3
Good Measurement Practices	4
EQUIPMENT REQUIREMENTS	4
CALIBRATION	6
INSTRUMENT CONFIGURATION	6
DEMODULATED RF SIGNALS	8
TERMINATION	8
DEFINITION OF THE PAL TELEVISION STANDARD	8
PERFORMANCE GOALS	8
Waveform Distortions and Measurement Methods	9
I VIDEO AMPLITUDE AND TIME MEASUREMENTS	9
Amplitude Measurements	10
Time Measurements	12
SCH Phase	15
II LINEAR DISTORTIONS	18
Chrominance-to-Luminance Gain and Delay	19
Short Time Distortion	24
Line Time Distortion	26
Field Time Distortion	28
Long Time Distortion	30
Frequency Response	31
Group Delay	36
K Factor Ratings	38
III NONLINEAR DISTORTIONS	41
Differential Phase	42
Differential Gain	46
Luminance Nonlinearity	50
Chrominance Nonlinear P h a s e	5 2
Chrominance Nonlinear Gain	5 3
Chrominance-to-Luminance Intermodulation	54
Transient Sync Gain Distortion	55
Steady-State (Static) Sync Gain Distortion	56
IV NOISE MEASUREMENTS	57
Signal-to-Noise Ratio	58
V TRANSMITTER MEASUREMENTS	6 0
ICPM	61
Depth of Modulation	63
GLOSSARY OF TELEVISION TERMS	64
APPENDICES
APPENDIX A - PAL COLOUR BARS	67
APPENDIX B - SINE-SQUARED PULSES